Fatty esters are a class of oil-phase materials that have been widely used for many years in the cosmetic and personal care industries. Often, because a primary use of these compounds is as an emollient, they are referred to as “mono-functional.” Related to this property is the ability to help reduce transepidermal water loss, enhance skin barrier function and improve skin hydration. In contrast, the fatty esters of the present invention are multi-functional—they provide emolliency (and its associated benefits) while at the same time effectively delivering antioxidants to the hair and skin. The latter property is attributable to the high concentration of antioxidants in the unsaponifiable fraction of shea butter, particularly MPSB, that is produced and maintained through the use of mild-processing steps, both in the preparation of the starting material (mild-processed shea butter) and its subsequent processing into the claimed MPSB ester derivatives.
Shea Butter is a butter extracted from the kernel of Butrospermum parkii. This plant, also referred to as Vitellaria paradoxa, is native to Africa. The term butter describes a material that is a solid at room temperature, but melts at about 40° C. Chemically, the butter is a triglyceride conforming to the following structure
wherein R1, R2 and R3 each have one of the following compositions:
R GroupCommon NameRange (%)Typical (%)C11H23Lauryl0.1–2.00.2C13H27Myristyl0.5–2.01.0C15H31Cetyl2.0–6.04.0C17H35Stearyl25.0–50.035.0C17H33Oleyl40.0–60.059.0C17H31Linoleyl0.5–1.00.8
The average composition of R2 is different than R1 and R3, the latter two being similar. The R2 moiety contains predominantly the unsaturated C18 group (oleyl) while R1 and R3 contain predominantly the saturated C18 group (stearyl). Differences between internal (R2) and terminal (R1, R3) substitution are seen in natural products but not in synthetic molecules produced in the laboratory.
The high levels of stearyl and oleyl groups make shea butter and its ester derivatives of particular interest in the personal care industry. While other raw materials used in personal care products have these species, the compounds of the present invention have significantly high concentrations of unsaponifiables, which posses highly desired antioxidant, ultra-violet radiation protection, and free-radical scavenging properties. MPSB of the present invention typically contains from about 5% to about 15% by weight of unsaponifiables. In contrast, other butters commonly used in personal care products have less than 2% unsaponifiables. For example, coca butter (from Theobroma cacao) averages 0.4% unsaponifiables and Illipe butter (from Shorea stenoptera) averages 1.1%.
The novel shea butter esters of the present invention are produced by reacting shea butter, preferably MPSB, preferably under specific conditions with fatty alcohols. By “mild processed” is meant processes that do not remove or otherwise diminish the amount or potency of active ingredients, particularly highly desired unsaponifiables. In one aspect of the present invention, mild processing is employed both at the time of harvesting and initial extraction and during subsequent preparation of derivatives. These mild processes result in materials containing unexpectedly high amounts unsaponifiables, notably antioxidants.
Fatty alcohols are widely-used in formulating cosmetic and personal care products, typically as emollients, emulsifiers and co-emulsifiers. They are higher molecular weigh non-volatile alcohols produced from natural fats and oils by reduction of the carboxylic acid group on a fatty acid to hydroxyl. Fatty alcohols prepared from naturally-occurring fatty acids normally contain an even number of carbon atoms. Synthetic fatty alcohols with equivalent physicochemical properties to naturally-derived products are also commercially available.
Fatty alcohols serve to prevent transepidermal water loss and can impart a smooth, velvety feel to the skin and are key ingredients in many shampoos and cleansing surfactants. As chemical intermediates, the primary uses of fatty alcohols include esterification, ethoxylation and sulfation to produce, among other materials, fatty sulfate salts and alcohol ethoxylates.
U.S. Pat. No. 5,646,321 teaches the reaction of a Guerbet alcohol with meadowfoam oil as a triglyceride, as meadowfoam methyl ester (the product of reaction with methanol) or as meadowfoam fatty acid to produce fatty esters that, because of the specific alkyl distribution of meadowfoam oil, are liquid at high temperatures and do not exhibit rancidity (e.g., resulting from the oxidation of a double carbon bond to form malodorous, bad-tasting, aldehydic compounds). The esters described in the '321 patent do not possess the desirable unsaponifiable fractions, and with them antioxidant properties, of the compounds of the present invention.